PmodALS™ Reference Manual
Revision: September 9, 2013
Note: This document applies to REV A of the board.
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Overview
The Digilent PmodALS demonstrates light-to-
digital sensing through a single ambient light
sensor. Digilent Engineers designed this Pmod
around the Texas Instruments ADC081S021
analog-to-digital converter.
Features Include:
• 3-wire SPI
TM
communication interface
• 8-bit resolution
Functional Description
The PmodALS utilizes a single ambient light sensor (ALS) for user input. The amount of light the ALS is exposed
to determines the voltage level passed into the ADC, which converts it to 8-bits of data. A value of 0 indicates a
low light level and a value of 255 indicates a high light level.
The ADC081S021 is placed in normal mode by bringing the CS pin low, and will deliver a single reading in
sixteen SCLK clock cycles.
SPI Interface
The PmodALS communicates through a 3-wire Serial Peripheral Interface (SPI) to deliver converted data from
the Texas Instruments ADC081S021. Note: The Texas Instruments ADC081S021 is read-only.
Table 1 describes the Pmod board header pin functions. These are the control signals as named on the
ADC081S021.
To establish a communication interface, connect the CS pin to the SS signal and the SDATA to the SDI signal on
the host board.
Users can access data from the ADC081S021 by reading in a 16-bit word via SPI. The ADC081S021 will produce
both leading and trailing zeros around the 8-bits of data. For more information on the leading and trailing
zeros, please refer to the device data sheet available at www.ti.com.
Digilent PmodALS
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Copyright Digilent, Inc. All rights reserved. Other product and company names mentioned may be trademarks of their respective owners.
Table 1
Connector J1- SPI Communications
Interface Connector Signal Description
Power Supply
Any external voltage applied to VCC must be kept between 2.7V and 5.25V to avoid damaging the PmodALS. It
is recommended to operate the board at 3.3V
Standard Pmod headers on Digilent boards provide both 3.3V and 5.0V power supplies for Pmods. Make sure
that the jumper next to the Pmod header is shorted to the 3.3V supply.
Note: For more information on the PmodALS, see the schematic at: www.digilentinc.com. For a detailed
review of the ADC081S021, including communication modes, please refer to the ADC081S021 Data Sheet
available at www.ti.com.
Pin Signal Description
1 CS Chip Select
2 NC Not Connected
3 SDATA Serial Data Out
4 SCLK Serial Clock
5 GND Power Supply Ground
6 VA Power Supply (3.3V/5V)
